Discharge-gap device



Mavrch 28, 1939. J. KA HODNETTE ET Al. 2,151,763

` DISCHARGE-GAP DEVICE V Filed Jan. 4, 1936 Z Z4- 7 g l2 INVENTOR5.

WITNESSES; v 4 John K Hoafnehe and mal/ AIS/a7? D. Forbes.

ATTORNEY Patented Mar. 19.39

UNITEDSTATI-:s PATNT oFFlci:A

John K. Hodnette and Allan D. Forbes, lSharon, Pa., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 4, 1936, Serial No. l51,554 5 Claims. (Cl. 175-30) Our invention relates to the mounting of discharge-gap devices ofthe type in which a discharge-arc is formed insidevof an'insulating tube of fibre or other material capable of evolving substantiallynon-ionized gases in the presence of an arc, with means for discharging the gases to the external atmosphere so as to extinguish the arc.

More particularly, our invention relates to'the means for mounting ksuch a discharge-gap device-'inside of the metal tank of a transformer,

. or other electrical apparatus, so that porcelain through a; portie' or other substantially non-vaporizable, weatherresistant insulating material is interposed between the discharge-gap device and the tank of the protected apparatus.

Our invention farther comprises means for providing an ext rnal arc-gap connection, in air,

from the inte lly mounted discharge-gap deo f the protected apparatus.

provision of means for providing an externally mounted series resistor for the internally mounted discharge-gap device previously mentioned, with special gap-means from -both terminals of the resistor to the outside of the tank of the protected apparatus.

With the object of providing the apparatus and securing the advantages referred to above,

hereinafter described, and claimed and 'lllus'- trated in the accompanying drawing, the single figure of whichsds a longitudinal sectional view cf an electrical apparatus to be protected, and the tank therefor, with'a disp charge-gap device mounted' therein in accordance with our invention. We have shown .our invention as applied to a transformer-tank i having one or mare highpotential bushings 2 therein, high-potential leads 3, windings 4, a magnetizable core 5, and oil 6` in which the transformer-windings 4 land core 5 are immersed. Mounted within the transformertank'l above the levelof the oil 6 is shown one of the protective devicesor tubes l, previously referred to, the same comprlsingan insulatorthe electrodes being sufliciently'sliort, as comvice just mentioned, to the outside' of the tankl pared to the external ashover-distance around the outside of the insulating tube 8, so that ashover will always occur inside the tube rather than outside thereof. The arcing space between the electrodes 9 and II is preferably lled with a multi-slotted diffuser-member I2 made of fibre or other arc-responsive volatizable insulating material.

In accordance with our invention, the vented electrode Il is provided with a metallic pipelike extension I3 extending beyond the insulating tube 8 -and extending through a hole or perforation I5 in the wall of the tank I, above the level of the oil 6 therein. At the place where the pipe-like extension !3 passes through the perforation I5 in the tank, said pipe-like extension is surrounded by a removable anged sleeve I8 of 4porcelain or other relatively non-volatizable. weather-resistant insulating material which fits into said perforation, with the flange I8 of the sleeve I 8 against the inside of the tankwall. A second sleeve 2li, also oi.' porcelain or other relatively non-volatizable, weather-resistant insulating material, surrounds the ilrst sleeve `III on the other side of the tank-wall, and is 'clamped thereto by suitable clamping means which are indicated as comprising a gasket 22 and a nut 23.

Inside of the tank, electrical connection is made with'the closed electrode 9 'by means of a highvoltage vjumper 2l which is connected to the high-potential lead 3. Outside of the tank, an effective surge-discharge connection is made to the end of the metallic pipe-like"v extension I3 through a resistor which is linsulatedly mounted on a bracket 3| by means of a porcelain or other insulator 32. 'I'he resistor 30 may comprise a block of molded composition-material which may consist of conducting orsemi-conducting particles and a more orless insulating binder. The bottom end of the` resistor 30. includes a metal sleeve 34 which is insulatedly mounted on the bracket 3i by means of the insulator 32, the interior 'of which -is partially niled with a plastic insulating compound 35. v'I'he outside of the metal sleeve 3l is spaced from the outside of the tank I by a gap 36, which is shown as terminating on a metallic bolt 3l attached to the tank. The top end of the resistor 30 is electrically connected td the free end of the pipe- `like electrode-extension I3 by means of a metal bracket-member or connector 39V which has a portion 40 which is spaced from the outside wall of the tank. l by a second gap M, which is longer than. the mst-mentioned gap 3E.

The resistor 3U is not necessary to be used. in every case. When it is used, its function is to limit the magnitude of the power-follow current which follows a lightning-surge discharge in the discharge-gap device 1.

When an excess-voltage surge appears on the high-voltage conductor 3 within. the tank l, the discharge-gap device l breaks down internally and flashes over, thus establishing a discharge-- current path from the conductor il through the Jumper 24 to the gap-device 1, and thence through the connector 39 to the resistor 3l! and through the short gap 36 to the wall of the tank l, from which the discharge continues to ground through a suitable surge-discharge path (not shown). When the excess-voltage surge has been discharged, power-current follows through the arc within the discharge gap-device 'l' and the arc at the external gap 36, usually until the first current-zero, at which time the kdeionizing action. of the blast in the discharge-gap device is sutilcient to extinguish the aro. In case of very excessive current-flow through the resistor 30, the same will eventually flash over, around its external surface. In order to prevent this, the second external gap 4I is provided, which will ilash over and form an arc ii' the ohmic voltagedrop in the resistor 30 should become eicessive.

It will be observed that our present invention provides means for making certain that the highA voltage lead 3 of the electrical device to be protected is not connected to the tank l by any insulating material which is subjected to the repeated plays of electric arcs or which is in any manner affected by Weather-conditions or responsive to an electric arc. The fibre, sometimes known as hard fibre, which is preferably utilized as the arc-responsive volatizable material, has appeared to be perfectly good, in its insulating qualities, even after an extremely large number of very severe discharges oi the discharge-gap device: but theoretically, at least, it is subject to a certain small amount of deterioration as a result of exposure to the arc, and it does evolve a certain quantity oi' semi-conducting carbonaceous particles, together with the substantially non-ionized insulating gases which it evolves. These conducting carbonaceous particles. have heretofore all been swept out of the tube by the blast resulting from each discharge, so that they have not been round to accumulate as conducting deposits on the inside walls oi the tube. Our invention provides a definite safeguard-means, however, whereby any possible risk in regard to the deterioration of the bre o1' the accumulation oi conducting deposits is avoided by means of our porcelain-mounting for the discharge-tube.

Furthermore, in previous applications of discharge-tubes to transformer-tanks, where the vented electrode was electrically connected to the tank, and where the series resistor 30 was, of necessity, therefore, mounted inside of the tank between the closed electrode 9 and the highvoltage lead 3, there was a likelihood of an occasional ilashover of the resistor, irl the space within the transformer-tank above the transformer oil. We have avoided the possibility of such a dis-- charge by insulating the vented electrode I i from the tank and by placing the resistor 30 outside et the tank in series electrical connection with the vented electrode I I, so that any resistor-nashover which occurs, as at our second or auxiliary exalcista teruel gap lil, will be outside of the tank, rather than inside the While We have illustrated our invention in a single preferred form of embodiment, it will be obvious that many changes may be made in the design and construction Without departing from the essential features oi our invention. We dei sire, therefore, that the appended claims shall be accorded the broadest construction consistent wit-l1 their language and the prior art.

We claim as our invention:

l. A self-extinguishing electrical dischargedevice comprising a tub-e of insulating gas-evolving arc-responsive material, a closed electrode associated with one end of the tube, a highpotential terminal connection fcrsaid closed electrode, a vented electrode associated with the other end of the tube, at least one of said elec trodes extending into the tube, an electrical ground connection for said vented electrode, said ground connection including a separate open-air series-gap means, and supporting means for said electrical discharge device, said supporting-means including Weather-resistant insulating material which is substantially unalected by an are, the series-gap means being in shunt relation to said weather-resistant insulating material.

52. An arc-interrupter comprising a tube of insulating material having one end closed and the other end open, electrodes spaced apart internally of said insulating tube and normally insulated from each other, the material of said insulating tube being adapted to volatilize on exposure to an arc to extinguish the arc and expel the gases from the open end of the'tubc, a metallic pipe-like extension of the electrode at the open end of the tube, said extensouextending beyond said tube of insulating material, a removable sleeve of substantially non-volatilizing insulating material surrounding said pipe-like extension, supporting-means surrounding said sleeve, and open-air series-gap means in shunt relation to said substantially. non-volatilizing insulating material.

3. In combination with an electrical apparatus having an enclosing metallic tank and a highpotential lead insulatedly passing through said tank, an excess-voltage protective-gap device mounted within said tank and clomprising a tubular insulator with an electrode for each end and with gas-evolving insulator-material for evolving gases in a spark-gap space between the electrodes within the tube when subjected to an electric arc, one of said electrodes comprising means for tightly closing its end of the tube, a conductor for electrically joining said electrode to said high-potential lead within the tank, the

'other electrode being tubular and having a me tallic tubular extension extending beyond said tubular insulator, at least one of said electrodes extending into the tube, a hanged sleeve of relatively ncn-volatizabie insulating material surrounding sald tubular extension, said tank having a perforation in a wail thereof for receiving said sleeve with its flange on one side of tankwall, a second sleeve, also of relatively nonvolatlzable insulating material, surrounding the first-mentioned sleeve 0n `theother side of the tank-wall and clamped thereto, and electrical vconnection-means including an open-air gapdevice outside ofthe tank interposed between said tubular electrode and the tank.

4. In combinationwith an electrical apparatus having an enclosing metallic tank and a highpotential lead insulatedly passing through said aisance tank, an excess-voltage protective-gap device mounted within said tank and comprising a tubular insulator with an electrode for each end. and with gas-evolving insulator-material for evolving gases in a spark-gap space between the electrodes within the tube when subjected to an electric arc, one of said electrodes comprising'A means for tightly closing its end of the tube, a conductor for electrically joining said electrode to said high-potential lead Within the tank, the other electrode being tubular and having a metallic tubular extension extending beyond said tubular insulator, at least one of said electrodes extending into the tube, a flanged sleeve of relatively non-volatizable insulating material surrounding said tubular extension, said tank having a perforation in a. Wall thereof for receiving said sleeve with its ange on one side of tankwall, a second sleeve, also of relatively nonvolatizable insulating material, surrounding the rst-mentioned sleeve on the other side of the tank-wall and clamped thereto, a resistor element outside oi the tank, and electrical connecting and mounting means for said resistor whereby one terminal of the resistor is connected to said tubular extension and electrically separated from the tank by an open-air gap of predetermined length, while the other terminal of the resistor is electrically separated from the tank by a shorter open-air gap.

5. The combination, with an excess-voltage protective element of a type capable of interrupting the arc following an excess-voltage discharge, of a conducting supporting-member, means for insulatingly mounting one terminal of said protective element on said conducting supportingmember, a resistor-element electrically connected, at one end, to said terminal of said protective element, and insulating mounting-means for said resistor-element whereby the end of the resistor-element which is connected to the protective element is electrically separated from said supporting-member by an open-air gap of predetermined length, while the other end of the resistor-element isl electrically separated from said supporting-member by a shorter open-air gap. y

JOHN K. HODNE'IIE. ALLAN D. FORBES. 

